Adding travis.yml and travis badge to README

No extra line

Fixing the badge url to point to master branch
Fixed readme to reflect updated gem version
Add README for Bundle Install via gemfile
use git for bundle install via gemfile
add Script#is_canonical_signature? draft

  TODO: finish and add tests. was just something i had on my local git stash.
add hash160_to_p2sh_address utility method
default script_sig_length and script_sig for initializing TxIn